Van Wijngaarden, W.A. and Syed, A. 2015. Changes in annual precipitation over the Earth's land mass excluding Antarctica from the 18th century to 2013. Journal of Hydrology531: 1020-1027.

Working with precipitation measurements made at nearly 1,000 weather stations located in 114 different countries -- each of which had at least 100 years of observations that resulted in a macro-dataset comprising over 1.5 million monthly precipitation amounts -- Wijngaarden and Syed (2015) developed a precipitation history for Earth's entire land mass (minus Antarctica), which they ultimately used to calculate global changes in precipitation for a set of different time intervals relative to the 1961-90 time interval. And what did these results reveal?

The two Canadian researchers report that "most trends exhibited no clear precipitation change," noting that "global changes in precipitation over the Earth's land mass excluding Antarctica relative to 1961-90 were estimated to be: -1.2±1.7, 2.6±2.5 and -5.4±8.1 percent per century for the periods 1850-2000, 1900-2000 and 1950-2000, respectively." In addition, they state that "stations experiencing low, moderate and heavy annual precipitation did not show very different precipitation trends," which would imply, as they describe it, that "deserts/jungles are neither expanding nor shrinking due to changes in precipitation patterns."

And they therefore also state, in the terminal sentence of their paper, that it is "reasonable to conclude that some caution is warranted about claiming that large changes to global precipitation have occurred during the last 150 years."